One way to check speaker polarity is to use a AA 1.5 volt battery, remove the speaker grill, and tap the wire to the battery and see if the woofer moves in or out , check all speakers the SAME way marked + to + and - to - ,
This should give you a good idea , But in a 2 or 3 way speaker systems the mid and or tweeter could be wired wrong from the woofer , done at the factory . So than this is problem.. lowes are stronger if all are in phase, highs are in the center of two speakers when in phase. I hope this helps in some way.
Just want to say what if all the speaker are out of phase thats ok too. Just as long as all the speakers are in phase with each other.. + may not be the same with all brands some times mixing brands of speaker could easly cause out of phase flags , but is easly identified / found with the battery test